Studies of the purification, mechanism of action and sequence of a new plasma protein SgP 120 have continued. Studies have continued on the role of complement in the destruction of parainfluenza virus. The mechanism by which antibody augments complement attack has been under continued study. The studies were broadened this year to include studies of vaccinia virus. Here a C4 binding protein like molecule is released from virally infected cells. The mechanism of action of this protein is under study. It has been shown that it has co-factor activity for C3 and C4 destruction and binds to both C3b and C4b.